Field of the Invention
This invention relates to an amorphous silicon solar battery possessing a high short-circuit current density.
A solar battery of this type in the known prior art comprises a flat substrate of glass or the like having a transparent electrode selected from indium oxide, indium tin oxide, tin oxide or the like formed thereon; an amorphous silicon semi-conductor layer comprising semi-conductor p-i-n layers formed on the transparent electrode; an indium tin oxide film in turn formed on the amorphous silicon semi-conductor layer for improving the adhesion between the semi-conductor layer; and a back electrode formed on the indium tin oxide film. This back electrode is formed by vapor-depositing a silver reflection film on the indium tin oxide film. This type of solar battery is not quite adequate, however, in that its short-circuit electric current density J.sub.sc is as low as 15 mA/cm.sup.2, in spite of the use of silver, which has a high reflective index.
A second known solar battery is disclosed in the Conference Record of the 16th IEEE Photovoltaic Specialists Conference (1982), by Deckmann et al pp 1425-1426. This solar battery is characterized by texturing the semiconductor with structures having characteristic dimensions nearly equal to the wavelength of visible light within the semiconductor so as to increase the short-circuit current thereof.
The Deckmann type solar battery may be prepared, for example, in such a manner that, as shown in FIG. 8, a single layer of spherical polyethylene latex of 0.1-0.5 micron in particle size is fixedly formed on the surface of a glass substrate, and the surface of the substrate a, having the latex layer as a mask, is formed into an uneven surface by applying an ion milling treatment to the surface, and thereafter, the uneven surface thus formed is coated with a silver film b to serve as a back electrode, a transparent conductive film c, an amorphous silicon semi-conductor layer d, and a transparent electrode film e, in sequence, in almost the same manner as mentioned above.
This type of solar battery is unsatisfactory, however, in that its short-circuit current density is not significantly improved, in spite of the difficult work entailed in forming the aforementioned uneven surface for causing a reflected ray from the back electrode to be confined in the semi-conductor layer, and there cannot be obtained thereby a high collection efficiency over a wide range of wavelength of a solar light.
In order to improve conventional solar batteries of this type, applicants have previously proposed that a transparent substrate be coated with a transparent electrode having an uneven surface with particles having an average grain diameter of 0.1-2.5 microns, an amorphous silicon semi-conductor layer, and a back electrode of silver, aluminum or the the like, in sequence, whereby there is obtained a solar battery having a slightly improved short-circuit current density, but of only 17 mA/cm.sup.2.
In the meanwhile, there has been hitherto known a type of solar battery such as disclosed in U.S. Pat. No. 4,400,577 or U.S. Pat. No. 4,419,533, etc. wherein there is interposed a layer of transparent conductive material such as ITO or SnO.sub.2 between the amorphous silicon body and a layer of reflective metal constituting a back electrode. It is, however, defective in that a high short circuit current density cannot be obtained thereby.